1. Performance of MLI Seams between 293 K and 20 K
Wesley Johnson and David Chato
Fluid and Cryogenic Systems Branch, Glenn Research Center
2019 Cryogenic Engineering Conference

2. Fundamental Approach for Developing Multilayer Insulation
MLI Blankets
Traditional
SS-MLI
IMLI
Hybrid

3. Fundamental Approach for Developing Multilayer Insulation
Penetration Integration:
NASA-TP
Seams
MLI Blankets
- Traditional
SS-MLI
IMLI
Hybrid

4. Fundamental Approach for Developing Multilayer Insulation
Skirt Integration
Penetration Integration:
NASA-TP
Seams
Repeatability
MLI Blankets
- Traditional
SS-MLI
IMLI
Hybrid
By accounting for each item separately, LOX ZBO testing accurately predicted total MLI performance. More information is needed for SHIIVER.
Tape, Pins & Attachments

5. Introduction
Performance is lost in multilayer insulation systems due to joints and seams in the insulation blankets:
Recognized as a concern since the introduction of multilayer insulation.
Insulating large tanks more seams required as the tank dimensions exceed the roll widths available
Over the years mitigation techniques have been developed:
These include overlapping every layer, or precision cutting to minimize the gap
However labor intensive and time consuming.
Shu investigated “cracks” in MLI in early 90s at liquid nitrogen temperatures
Recently Fesmire and Johnson re-examined the seams issue with a liquid nitrogen test rig at KSC and confirmed many of the previous findings.
This effort extends the seams work into liquid hydrogen temperatures and studies a broader range of proposed seam configurations.

6. Calorimeter Description

7. Test Matrix Test Number Description MLI Layers Seam Construction
Offset, x, (in) 1
Overlap seam 50
1 stagger 2
Interleaved Seam
N/A 3
Butt seam
Straight 4 5 6 20 7
Overlap Seam 8
Butt Seam 9

8. Blanket Descriptions Feature Yetispace Existing Blankets
Number of layers (total) 20 50
Number of sub-blankets 2
Number of layers per sub-blanket 10 25
Reflector Substrate
Polyester
Reflector Deposited Metal
Aluminum
Reflector thickness
mm (0.25 mil)
# spacers thicknesses per reflector
Spacer Material
Dacron B2A
Spacer Thickness mm
Covers thickness
5 mil
Design Sub-blanket Thickness
0.42 cm
1.59 cm
Design layer density
24 lay/cm
16 lay/cm

9. Typical Test Results (1/2)

10. Typical Test Results (2/2)

11. 50 Layer Test Results Overlapped seams out performed butt seams
Offsetting butt seams didn’t seem to provide any benefit
By the time the butt seam is handled, radiation path becomes torturous
Minimal difference between the best and worst seams
Test Number
Run
Qtotal, watts
Tavg, K
Kavg, W/m/K
DT, K
Qnet, W
dQ, W
dQ, W/m 1
Overlap Seams
0.788
21.06
29.8
2.56
0.786
0.040
0.044 2
Interleaved
0.748
19.16
27.3
2.43
0.746
0.000  3
Full Butt
0.806
18.85
26.9
2.51
0.802
0.056
0.061 4
Butt 2" Offset
2.52
0.803
0.057
0.062 5
Butt 4" Offset
0.810
19.37
27.8
0.807
0.067

12. 20 Layer Seam Results
Once again, Overlap seam out performed butt seam.
Minimal heat gains into system
Offsetting butt seams didn’t provide any benefit
Much bigger difference between the best and worst seaming configurations
Test Number
Run
Qtotal, watts
Tavg, K
Kavg, W/m/K
DT, K
Qnet, W
dQ, W
dQ, W/m 6
Interleaved
1.033
20.38
28.9
3.49
1.012
0.000 7
Overlap
1.035
18.62
26.6
3.65
1.015
0.003 8
Butt 2" Offset
1.222
17.52
25.0
4.21
1.199
0.187
0.205 9
Full Butt
1.160
17.25
24.7
4.09
1.146
0.134
0.147

13. Conclusions Measured heat loads for the nine tests conducted.
Layer by layer interleaved joint showed the lowest heat leak.
Overlap joint out performed the straight and staggered butt joints.
Surprisingly staggering the butt joint did not decrease the heat load
Increasing the stagger distance didn’t help.
In fact the test with the largest stagger was worse than straight butt joint, (although this may be due to damage incurred by repeated handling rather the joint itself).
Technician installed by “stitch taping” joints every ~5 layers, may have shown that stitch taping is as good as full taping
Even worst performing seam only 5% more heat leak than best performing seam at 50 layers
There are significant differences between 20 layers and 50 layers. This shows that the impact of seams is reduced with increased numbers of layers.

14. Questions?